From the prior art, numerous methods for coating the surface of a metallic substrate are known. For this, various known precursors, typically organoalkoxysilanes, zirconium alkoxides, and organic acids acting as complexing agents in an alcohol solution, for instance of ethanol or isopropanol, are used. Handling such methods is disadvantageous, not least because of the use of the alcohols mentioned, since their boiling points are comparatively low. Among other effects, this means that because of changes in concentration, the coating process becomes less controllable. Accordingly, comparatively great technical effort and expense must be employed in order to be able to meet workplace-relevant regulations in terms of safety and health. To improve the method, U.S. Pat. No. 5,939,197 shows a method for surface treatment of metal, especially of titanium and aluminum alloys (for instance the AA 7xxx group), for which various aqueous solutions of organoalkoxysilanes and zirconium alkoxides are proposed. In this method, zirconium alkoxides with short-chain organic radicals or mixtures with various chemical additives are used, as well as an organoalkoxysilane with a reactive organic group and acetic acid. The organoalkoxysilanes are intentionally those that have short alkoxysilane radicals that comprise 2 to 5 carbon atoms; one of these four radicals has an additionally chemically reactive group, such as a 3-aminopropyl or a 3-glycidoxypropyl radical. In this way, the attempt is made to make a coating available that adheres well and is durable. Nevertheless, such a method proves disadvantageous, since in the mixing of the starting compounds, a two-phase system first forms, which requires several hours to homogenize. Moreover, alcohols with a low boiling point, which are formed in the course of the sol-gel process or are added as solvents, worsen the controllability of the method because of a constant change in the composition of the reaction mixture. Furthermore, volatile alcohol vapors are potentially quite dangerous.